1. Field of the Invention
This invention relates to rigidized 1,3-oxazoles and a method for their synthesis. Additionally, this invention relates to the use of rigidized 1,3-oxazoles to form lasing media useful in dye lasers.
2. Description of the Prior Art
2,5-Diaryl-1,3-oxazoles and certain salts derived from those compounds are useful as laser dyes. The synthetic methods available for the preparation of those compounds all involve multistep syntheses with relatively low overall yields. A one-step synthesis of 1,3-oxazoles is known. This synthesis involves the reaction of ketones with nitriles in the presence of cupric triflate as an oxidizing agent. In a typical procedure, the ketone is added dropwise to the cupric triflate in refluxing nitrile containing a trace of an acid catalyst. The oxazole forms a complex with the cuprous triflat by-product and must be separated by thermalization and vacuum distillation, steam distillation with excess benzonitrile, or extraction of the copper salts with concentrated ammonium hydroxide.
The one-step synthesis for the production of 1,3-oxazoles is limited to those cases where the nitrile can be used as the solvent. The procedure is unsuccessful with a 1:1 molar ratio of ketone to nitrile in ethyl acetate at room temperature, or in refluxing glyme or in refluxing diglyme. The use of extended reaction times in the synthesis at 1:1 mole ratios results in the formation of polymeric materials.